Fix trim bar handles not visible

Bug from screenshot: trim bar visible but red handles not showing.

Causes:
1. video_duration in job is None for old jobs (was not saved on initial
   processing). Without it, fallback was endInit+60 which placed handles
   off-screen.

2. videoDuration was const, couldn't be updated when video metadata loads.

3. Handle offset was 9px but handles are now 24px wide (need 12px offset).

Fixes:
- Backend /api/transcript: fallback to last segment end time if
  video_duration missing in job
- Frontend: videoDuration is let, updated on loadedmetadata
- Handle offset 9px → 12px for 24px wide handles
- Re-render trim after metadata loads to pick up actual video.duration

app/main.py

@@ -1262,11 +1262,15 @@ async def get_transcript(job_id: str, user: str = Depends(check_auth)):
         analysis = json.loads(analysis_path.read_text())
         transcript = analysis.get("transcript", {})
         clip_range = analysis.get("clip_range", {})
+        # video_duration: probaj iz analysis, sicer iz zadnjega segmenta, sicer 0
+        video_dur = analysis.get("video_duration") or job.get("video_duration") or 0
+        if not video_dur and transcript.get("segments"):
+            video_dur = max((s.get("end", 0) for s in transcript["segments"]), default=0)
         return {
             "segments": transcript.get("segments", []),
             "language": transcript.get("language", "?"),
             "clip_range": clip_range,
-            "video_duration": job.get("video_duration", 0),
+            "video_duration": video_dur,
         }
     except Exception as e:
         raise HTTPException(500, f"Napaka pri branju: {e}")